Thermo-electric overload safety switch and indicator systems



July 17, 1956 M. l. HERTAN THEIRMO-ELECTRIC OVERLOAD SAFETY SWITCH AND INDICATOR SYSTEMS Filed July 13, 1953 3 Sheets-Sheet l FLQ. 2.

FAQ. 3.

INVENTOR Melvin Irwin Herl'am ATTORNEY y 7, 1956 M. l. HERTAN 2,755,361

THERMO-ELECTRIC OVERLOAD SAFETY SWITCH AND INDICATOR SYSTEMS Filed July 13, 1953 5 Sheets-Sheet 2 INVENTOR Mel v in, Irwin Herban/ ATTORNEY y 7. 1956 M. 1. HERTAN 2,755,361

THERMO-ELECTRIC OVERLOAD SAFETY SWITCH AND INDICATOR SYSTEMS Filed July 13, 1953 3 Sheets-Sheet 3 INVENTOR Me [vi/Z 11' win Herfarz,

7 ATTORNEY United States Patent THERMO-ELECTRIC OVERLOAD SAFETY'SWITCH AND INDICATOR SYSTEMS Melvin I. Hertan, Brooklyn, N. Y., assignor of one-half to Alan G. Golby, Brooklyn, N. Y.

Application July 13, 1953, Serial No. 367,594

6 Claims. (Cl. 200-140) This invention relates to a system for controlling the operation of an electric circuit in response-to .a stimulus, which may for example be electrical, thermaL'or mec'hanical. More specifically, this invention relates to protective devices wherein an electric circuit .is opened or closed .upon .theoccurrence of a predeterminedcondition, suchias an .overload.

Because .of its unique construction, the invention has diverse applications. It may be employed in an automotive electrical system to prevent generator burn outs and .to indicate excessive charging or overloading. Conventional regulators, while controlling the voltage and current of automotive electrical systems, do not prevent generator burnouts, or provide an indication of overcharging or overloading.

The invention may also be employed to interrupt the connection of a generator and its load or to complete a circuit between .a motor and its source of power. In either case, operation of the invention may be made dependent upon the existence of predetermined conditions. The invention is ideally suited for protective functions in :an oil burner system.

Moreover, the invention may be employed as a control, indicator, or alarm in a pressure system, such as a steam boiler or refrigeration unit.

Accordingly, it is an object of the invention to provide a novel circuit controller.

It is an additional object to provide a device for making .or breaking an electric circuit upon the occurrence of predetermined conditions.

A further object is to provide a novel thermo-electric switch.

Another object is to provide a novel pressure responsive switch.

Yet another object is to provide a unique circuit breaker which operates on the principle of volumetric expansions.

A more specific object is to provide a system for preventing generator burn outs and for indicating the existence of an overload.

A further object is to provide in a system wherein a generator charges a battery, a device for preventing overcharging.

Another specific object of the invention is to provide a unique system wherein a relay is operated upon the existence of predetermined criteria.

Still another object of the invention is to provide a novel system of oil burner protection.

A more specific object is to provide a system of oil burner protection wherein the pump motor is maintained inoperative in the event that the ignition transformer fails.

An additional specific object is to provide a system of oil burner protection wherein the pump motor is deenergized if it becomes overloaded.

Still another object of the invention is to provide an overload safety switch and indicator which does not add appreciable resistance to an electric circuit.

2,755,361 Patented July 17, 1956 Yet another object is -to provide an adjustable circuit controller which may energize by either alternating or direct current of predetermined magnitude.

A further object of the invention is to provide a positive acting circuit breaker which eliminates the possibility of sticking contacts due to arcing.

These and other objects of the invention will be elucidated in the following description of the invention considered together with the accompanying drawings wherein:

Fig. 1 is a .partly schematic representation of the invention employed as automotive electrical system protection.

Fig. 2 is a sectional view of the unique switch construction embodied in the invention.

Fig. 3 is a modification of the switch construction.

Fig. 4 is a schematic diagram of the invention employed to control the connection of a source of power to a load.

Fig. 5 is a schematic diagram of the invention incorporated in an oil burner system; and

Fig. 6 illustrates a modification of the switch unit employed in a fluid pressure system.

Referring to the drawings, particularly to Figs. '1 and 2, the switch unit comprises a hollow cylindrical casing 10 which may be composed of brass, for example. Inside the tube is a bellows 11, which may be constructed of flexible metal, containing an expansive fluid, either gas or volatile liquid. The bellows has a continuous surface and is sealed at each end as by brass disks 12 and 13, which may be brazed or soldered to the metal bellows. The disk 13 is fitted to the inside diameter of the cylinder 10 and serves to center the bellows assembly and to maintain adequate clearance between the bellows and the inner wall of the cylinder. The outside diameter of disk 12 may be substantially the same as the outside diameter of'the bellows.

Disk 12 is provided with a central partially drilled bore 14 which receives one end of a rod 15, which may be threaded into the bore. Hermetic continuity of the bellows assembly is ensured by drilling bore 14 only partially through the disk 12. Rod 15 passes through a central bore 16 provided in a cylindrical fiber plug 17, which acts as a guide for rod 15 and an insulating mounting for metal contact washer 18, which is secured to the plug as by screws 19. Plug 17 is fitted to the inner surface of the cylindrical casing 10 and is held thereto by pins 20. A metal ball 21, which normally is seated in a central aperture 22 formed in washer 18, has a partially drilled bore 23 which may be threaded to receive one end of rod 15. The rod centers ball 21 in aperture 22 and ensures perfect circumferential contact between the ball and washer 18. A coil spring 24, attached at one end to ball 21 and encompassing a centering cone at its other end, biases ball 21 against Washer 13. The centering cone is provided with a central partially drilled bore 26 into which an adjusting screw 27 is secured. The adjusting screw is threaded into a metal block 23, which is partially split as indicated at 29. Block 2t is attached to the end closure disk 30 which has a central bore and may be held in place by pins 31. A set screw 32, threaded into block 28 locks adjusting screw 27 by applying a stress between the separate portions of the block. It is clear that the compression of spring 24 may be regulated by movement of adjusting screw 27 and that the setting may be maintained by virtue of set screw 32.

Lead wires 33 and 34 are connected to washer 18 and casing 10, respectively. Wire 33 passes through and is insulated from end plate 30, while wire 34 may be grounded as indicated. It is clear that an electrical circuit between wires 33 and 34 is completed whenever ball 21 contacts washer 18. This circuit may include either rod 15 and bellows 11, or spring 24, cone 25, and screw 27, or both groups of elements.

A bifilar coil 35, which may be a doubled length of copper wire insulated with heat resistant material, is wound upon the casing 10. The coil is one continuous wire and is non-inductive so that if the invention is employed in an alternating current system, induction heating will be substantially eliminated. A pair of heat resistant fiber coil retainer washers 36 may be provided to keep the coil in place.

Referring particularly to Fig. 1, one application of the principles of the invention is illustrated. Lead wire 34 is connected to one terminal of an automotive generator 37 through the contacts of a generator cut out relay generally designated 38. Lead wire 33 is connected to one terminal of coil 35, While the other terminal of coil 35 is connected to the opposite terminal of generator 37 through ammeter 39 and the conventional auto battery 40. An eight volt incandescent indicator lamp 41 may be connected across points XY, as shown.

In operation, the generator cut out is normally closed and charging current passes through coil 35. Lamp 41 is substantially dark, because its relatively high resistance is shunted by the relatively low resistance of the coil. The normal charging current creates a certain amount of resistive heat in the coil which is dissipated to the body of the thermoswitch. Adjusting screw 27 is set to create a compression in spring 24 which is sufiicient to maintain ball 21 in contact with washer 18 for normal charging currents. In other words, the volumetric expansion of fluid in bellows is not suflicient to overcome the force of the spring and unseat the ball. If the current output of the generator should increase beyond a predetermined threshold, however, the heat produced would be suflicient to displace the ball and break the circuit through the coil 35. The removal of the low resistance shunt constituted by the coil would then cause the lamp 41 to glow brightly. Lamp 41 serves two purposes: first to indicate overloading, and second, to place a high resistance in series with the generator to limit its output. It is evident that when the abnormal conditions have ceased to exist, the bellows 11 will contract, and the circuit through coil will be reclosed.

Fig. 4 illustrates another system according to the invention, wherein the thermoelectric switch is in a circuit with a high current load 46. A series circuit is shown including generator 47, load 46, coil 35, and contacts 48 of relay 49. The coil of relay 49 is connected across the generator through the thermoswitch. An indicator lamp 50 is shunted across the relay 49.

In operation, the thermoswitch is normally closed, thus causing a current to pass from the generator through the relay coil, closing contacts 48. The load is then energized, and indicator lamp 50 is out because shunted by. contacts 48 of relay 49. Normal currents through the load are insutficient to open the thermoswitch. If the current through the load increases or if the load is short circuited, the thermoswitch will open, thereby deenergizing the relay and opening the load circuit. Simultaneously the indicator lamp will glow, because the shunt thereacross is removed. If the abnormal conditions disappear, the circuit will automatically reclose. This circuit is sensitive, positive acting, and contains no appreciable resistance due to the circuit breaker. Moreover, it is completely automatic and gives an indication of its condition.

Fig. 3 illustrates a modification wherein the switch closes upon expansion of the bellows. Reference numerals identical with those of Fig. 2 have been used to designate corresponding elements. It will be noted that the embodiment of Fig. 3 difliers from that of Fig. 2 first in that the position of washer 18 with respect to plug 17 has been reversed. Washer 18 is provided with a circular depression 42 supplementing a small central bore 43 in place of the large central aperture 22 of Fig. 2; this arrangement may also be used in the latter embodiment. Ball 21 is drilled completely through and is secured to rod 15 adjacent washer 18 as by a pin 44. An additional centering cone 45 is secured to the end of rod 15 which formerly held ball 21 and receives the expansive force of spring 24.

It is clear that expansion of bellows 11 will cause ball 21 to contact washer 18 and close a circuit (not shown) connected as in Fig. 2. A coil (not shown), such as coil 35 in Fig. 2, may be provided to supply a thermoelectric stimulus.

Fig. 5 illustrates an embodiment of the invention incorporating the switch construction of Fig. 3 in an oil burner circuit. A generator 51 supplies power to the pump motor 52 and ignition transformer 53. The primary winding 54 of the ignition transformer is connected in series with the generator 51, a line switch or thermostatic room switch 55, and the coil 35 of the thermoswitch. The secondary winding 56 is coupled to a spark gap 57. Pump motor 52 is connected in a series circuit including generator 51, line switch 55, and the contacts 58 of a relay 59. An indicator lamp 60 may be shunted across the pump motor. The coil of relay 59 is connected in series with the generator and the thermoswitch.

In operation, when the line switch 55 is closed, current passes from the generator through the primary winding 54 of the ignition transformer and through coil 35. If there is no break in this circuit, that is if the primary winding is not open, the thermoswitch will close, thereby energizing the relay and closing the pump motor circuit through contacts 58. The indicator lamp will glow, indicating that the pump motor is energized. In the event that the transformer circuit opens, the thermoswitch will open, deenergizing the relay and opening the pump motor circuit. This action ensures that the ignition transformer is energized before the pump motor opcrates, thereby preventing dangerous oil pools which might accumulate if the pump motor were operating without energization of the ignition transformer.

It may be desirableto incorporate the protective system of Fig. 4 in the circuit of Fig. 5 in order to provide overload protection for the pump motor. This may be accomplished by connecting the thermoswitch, indicator lamp, and relay of Fig. 4 in circuit with the generator of Fig. 4, substituting the pump motor for the load 46. Thus, if the pump motor is overloaded, as might occur if the oil viscosity increased, contacts 48 will open and disconnect the motor from generator 51.

Fig. 6 illustrates another embodiment of the invention. The switch is basically similar to those illustrated in Figs. 2 and 3 and only the parts necessary to the explanation are illustrated. Here the stimulus is fluid pressure rather than electricity. The pipe 61 may, for example, carry steam or a refrigerant. The casing 10 and centering disk 13 are provided with a threaded bore 62 which communicates with the interior of the bellows 11. The bore 62 may be designed to receive a standard pipe fitting, illustrated by T 63, and to form a sealed connection therewith. The thermoswitch may be the type illustrated in Fig. 2 or the type illustrated in Fig. 3.

In operation, if the fluid pressure changes beyond a predetermined threshold, the electrical circuit including wires 33 and 34 will be either closed or opened depending upon the type of switch employed and the sense of the change. It is clear that the thermoswitch of Fig. 6 may be provided with all of the adjustable features disclosed source of heat may be employed to operate the thermoswitch. The switches may be employed in groups, with individual switches adjusted to particular thresholds of operation. They may be employed to actuate indicators, alarms, or relays, or they may themselves serve as circuit breakers. The differential fluid pressure inside the bellows and in the surrounding chamber may be controlled by partially evacuating the chamber or by inserting an inert gas or liquid therein, and the entire switch structure may be hermetically sealed, if desired.

Having thus set forth and disclosed the nature of this invention, what is claimed is:

l. A pressure responsive electrical switch comprising a hollow cylindrical metal casing having closed ends, an elongated conductive bellows in said casing having one end fixed electrically and mechanically to one end of said casing and the other end of said bellows movable relative thereto, an electrically conductive rod connected to said last bellows end and extending longitudinally of said casing, a conductive ball fixed to said rod, an insulator sleeve fixed interiorly of said casing, a conductive washer fixed to said insulator sleeve and insulated thereby from said casing, said rod passing through said insulator sleeve and said washer and insulated from said washer, said ball located adjacent said washer, spring means coupled to said rod for biasing said rod longitudinally, means for adjusting the compressive tension of said spring, lead wires coupled to said washer and said casing respectively, and means for causing said movable bellows end to move relative to said fixed end.

2. The switch as set forth in claim 1, wherein last named means comprises an expansive fluid in bellows, and means for changing said fluid pressure.

3. The switch as set forth in claim 2, wherein said said said 6 last named means comprises a source of thermal energy.

4. The switch as set forth in claim 3, wherein said source comprises a non-inductive coil wound about said casing.

5. The switch as set forth in claim 1, wherein an exterior source of fluid is coupled to said bellows.

6. A bellows actuated circuit maker and breaker comprising, a hollow metallic casing, an electrical heating coil circumferentially surrounding said casing, an expan sible and contractible fluid containing a convoluted tubular member within said casing, one end of said tubular member attached to one end of said casing, one end of said tubular member being movable, the movable end of said tubular member having one end of a metallic rod attached thereto, the other end of said metallic rod having a metallic ball attached thereto, a fiber insulating plug within said casing having an aperture for said rod to extend therethrough, said fiber insulating plug having a metallic washer attached thereto, said metallic washer having an aperture for said rod to extend therethrough, said aperture of said washer being of greater diameter than said rod, said metallic ball and said metallic washer being two electrical contacting members of said bellows actuated circuit maker and breaker,

References Cited in the file of this patent UNITED STATES PATENTS 1,542,722 Pinnell June 16, 1925 1,559,022 Wensley Oct. 27, 1925 1,639,888 Hawkins Aug. 23, 1927 1,661,794 Fogarty Mar. 6, 1928 2,064,436 Mantz Dec. 15, 1936 2,336,400 Isserstedt Dec. 7, 1943 

